1. Field of the Invention
The present invention relates generally to wireless communications, and more particularly, to applying a ciphering configuration by entities in a wireless communication network.
2. Description of the Related Art
In Universal Mobile Telecommunications System (UMTS), data flow on any connection, known as a radio bearer, between a User Equipment (UE) and an UMTS Terrestrial Radio Access Network (UTRAN) can be ciphered i.e., encrypted, at any point in time, under control of the UTRAN.
Typically, the UTRAN a starts or stops ciphering, or changes a ciphering configuration by sending a Security Mode Command (SMC) including ciphering information to the UE. The ciphering information includes a ciphering mode, a ciphering key, an activation time associated with a receiver and a transmitter, and a Hyper Frame Number (HFN). The ciphering activation time is a logical sequence number at which the UE and the UTRAN both apply a new ciphering configuration used on that radio bearer in a given direction, i.e., either uplink or downlink. This synchronizes the UE and the UTRAN, and facilitates a smooth ciphering changeover without undue delay.
According to the 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 25.331 V10.1.0, a UE and a UTRAN are to ignore an activation time associated with a new ciphering configuration, and apply the new ciphering configuration in both uplink and downlink immediately after a reset or re-establishment procedure.
However, when a UE applies a new ciphering configuration in an uplink and sends an Acknowledgement Mode (AM) Data (AMD) Protocol Data Unit (PDU) to the UTRAN, which gets lost or delayed, e.g., due to an interruption caused by a reset or re-establishment procedure, a UTRAN may initiate a reset procedure and discard any incoming AMD PDUs from the UE during the reset procedure. As a result, the UTRAN may not be able to apply a new ciphering configuration in the corresponding downlink.
Additionally, during a reset procedure, the UE and the UTRAN synchronize an HFN in the uplink and the downlink. However, as per the 3GPP TS described above, the UE and the UTRAN ignore the activation time and apply the new ciphering configuration in the uplink and the downlink, thereby losing synchronization of the HFN in the uplink and downlink.
Further, HFN synchronization may also be lost due to a re-establishment procedure performed when initializing peer Radio Link Control (RLC) entities in the UE and/or the UTRAN.